BACKGROUND: Increased intraocular pressure (IOP) in the eye is a primary risk factor for development and progression of primary open angle glaucoma (POAG). Increased IOP partially results from increased resistance to aqueous humor outflow in the trabecular meshwork (TM). One of the candidates that significantly contribute to increased resistance to aqueous humor outflow is thrombospondin-1 (TSP-1), which functions as a remodeler of cell-matrix interactions. TSP-1’s most significant function is activating transforming growth factor-beta2 (TGF-β2), which stimulates extra-cellular matrix (ECM) secretion in the TM, resulting in increased resistance to aqueous humor outflow. Previous studies have shown that a steroid dexamethasone (DEX) treatments for five weeks significantly increases IOP in mice. This study tested the hypothesis that DEX treatment for five weeks will increase the expression of TSP-1 and TGF-β2 in the TM compared to the saline treatment in WT and TSP-1 deficient (TSP-1-/- ) mice, and that there is a positive correlation between the expression of TSP-1 and TGF-β2 and IOP.
METHODS: Wild type (WT) and TSP-1-/- mice were divided into saline or 0.1% DEX groups (n=42 per group). The treatments were administered twice a day through eye drops. 14 mice (equal amounts of females and males) from each group were sacrificed at weeks 1, 2 and 5 respectively. Six randomly selected eyes (equal amounts of males and females) from each group were then enucleated, cryo-sectioned and processed for immuno-staining to analyze the expression of TSP-1 and TGF-β2. The intensity of the staining in the TM, ciliary body (CB) and corneal epithelium (CE) were analyzed using ZEN© software.
RESULTS: The staining intensity of TGF-β2 was significanlty increased in the TM in WT and TSP-1-/- mice treated with DEX at the end of five weeks compared to mice treated with saline. The staining intensity of TSP-1 also significantly increased in the TM in WT mice treated with DEX at the end of five weeks compared to mice treated with saline. There is a significant positive correlation between mean IOP and mean TGF-β2 (R2=0.8255, P< 0.001) and mean TSP-1 (R2=0.8590, P< 0.01) staining intensity in the TM over the course of five weeks. There was no significant positive correlation between TGF-β2 and TSP-1 staining intensity in the TM when plotting the raw data (R2= 0.0350, P> 0.05). There were no significant differences in TGF-β2 staining intensity in the CB and CE in WT and TSP-1-/- mice treated with either DEX or saline (P> 0.05). There were also no significant differences in TSP-1 staining intensity in the CB or CE between WT mice treated with DEX or saline (P> 0.05).
CONCLUSION: The results support the hypothesis that TSP-1 and TGF-β2 expression in the TM is positively correlated to IOP, suggesting that both TSP-1 and TGF-β2 signaling play an important role in regulation IOP by affecting aqueous outflow via the TM.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/43751 |
| Date | 31 January 2022 |
| Creators | Williams, Gregory |
| Contributors | Gong, Haiyan |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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